Fluids (Like the background?)

What is a fluid? Materials that flow and have no definite shape of their own.

Pressure Force exerted on a surface P = Force / surface area ; P = F/A. Unit of measure = Pascal (Pa), aka 1 N/m2

Pressure Example Problem A child weighs 364 N and sits on a 3-legged stool, which weighs 41 N. The bottoms of the stool’s legs touch the ground over a total area of 19.3 cm2. What is the average pressure that the child and stool exert on the ground? How does the pressure change when the child leans over so that only two legs of the stool touch the floor?

Gas Laws Boyle’s Law Combined gas law Ideal gas law Charles’s Law PV = constant P1V1/T1 = P2V2/T2 P1V1 = P2V2 Ideal gas law Charles’s Law PV = nRT V/T = constant n=number of moles present V1/T1 = V2/T2 R = constant, 8.31 (Pa* m3)/(mol*K)

Gas Laws

Gas Law Example Problem A 20.0 L sample of argon gas at 273 K is at atmospheric pressure, 101.3 kPa. The temperature is lowered to 120 K, and the pressure is increased to 145 kPa. What is the new volume of the argon sample? Find the number of moles of argon atoms in the sample. Find the mass of the argon sample. The molar mass of argon is 39.9 g/mol.

Thermal Expansion When heated, all forms of matter – solids, liquids, and gases – generally become less dense and expand to fill more space. When air near the floor of a room is warmed, gravity pulls the denser, colder air near the ceiling down, which pushes the warmer air upward. (aka heat rises!)

Where do we use thermal expansion?

Plasma Heat up a solid? Turns into a liquid. Heat up a liquid? Turns to gas. What happens when you heat up a gas? Gas-like state of negatively charged electrons and positively charged ions Plasma can conduct electricity! Most matter in the universe is actually a plasma

Plasma

Forces within liquids Cohesive forces Adhesive forces Electromagnetic force of attraction between fluids Result in surface tension among particles of liquids Why water droplets are almost completely spherical Adhesive forces Electromagnetic attractive forces that act between particles of different substances Meniscus of water in a graduated cylinder

Cohesion vs. adhesion

Evaporation and Condensation Fast-moving particle that can break through and escape the surface layer Increase the kinetic energy by increasing temperature Condensation When particles that have evaporated into the air return to the liquid phase if kinetic energy or temperature decreases

Viscosity Measure of internal friction in a liquid

Volatile Liquid A liquid that evaporates quickly

Why does a humid day feel warmer than a dry day at the same temp? On a humid day, the water vapor content of the air is high. Because there is already a lot of water in the air, water molecules in perspiration are less likely to evaporate.

Fluids at rest still produce a force Pascal’s principle Any change in pressure in a fluid applied at any point on a confined fluid is transmitted and undiminished throughout the fluid F2=(F1A2)/A1

Force Exerted by a Hydraulic Lift Dentists’ chairs are examples of hydraulic-lift systems. If a chair weighs 1600 N and rests on a piston with a cross-sectional area of 1440 cm2, what force must be applied to the smaller piston, with a cross sectional area of 72 cm2, to lift the chair?

Swimming under pressure Pressure of water on a body (column of water) Pressure exerted on a submerged object by a column of water. Pressure = density of fluid * height (or depth of water) * acceleration due to gravity P = ρhg

Swimming under pressure

Example problem How much pressure must a submarine withstand at a depth of 120.0 m? The density of water is 1,000 kg/m³.

Buoyant force (Archimedes’ principle) An object immersed in a fluid has an upward force on it that is equal to the weight of the fluid displaced by the object. Does not depend on the weight of the object, only the weight of the displaced fluid. Fbuoyant = ρfluidVg

Buoyant force (Archimedes’ principle)

Example problem A 0.001 m3 granite building block is submerged in water. The density of granite is 2.70 x 103 kg/m3. What is the magnitude of the buoyant force acting on the block? What is the apparent weight of the block?

Fluids in motion Bernouille’s principle As the velocity of a fluid increases, the pressure exerted by that fluid decreases

Streamlines How to represent the flow of fluids around objects

Create 15 question quiz for your classmates to take to help study for the test 3 of the questions should include a picture, graph, and a chart for your quiz-taker to use It does not count if you ask your classmates to create one 1 question should be a short answer, the rest should be multiple choice (with A, B, C, and D answer choices). “Short answer” means that they can answer the question in 2-3 sentences. Questions should be from Genetics notes Must include an answer key with the correct answers. You can get BONUS points on your test if I use your question on Jeopardy 

Extra Points on Your Test! All 15 questions with answer key 7 extra points 3 people to take your quiz Each person who takes your quiz will earn you 1 extra point